I don't agree with either of you 2 guy's, if you do the Job correctly the amount of muck sprayed out can be kept to a minimum, Take a look at the 2 pictures over half way through a run, and almost to the end, look at the amount of muck running down the facias? very little.
I first check with CCTV what its like up there, if its bad I use the gutter scoop I made and then I run the gutter tool with the white nozzle fitted, I use it like a brush and sweep it along to the downpipe.